Two bacterial systems will be studied in order to define in molecular terms the precise mechanisms that regulate the functioning of the genetic material in Salmonella. In the first system, the histidine operon, we will attempt to construct a molecular map through DNA-DNA hybridization studies. Also, we will attempt to pin-point the operator- promoter region, for we believe it to be large enough for electron microscope visualization and to possess a unique conformation. In the second system, flagellar synthesis and chemotaxis, we will pursue genetic and physiological studies on factors influencing flagella formation and those involved in the bacterial response to chemoattractants.